This project is a longitudinal study of the relationships among PTH, sex hormones, biochemical markers of bone turnover, bone histomorphometry, cytokine gene expression and production, and bone density. The subjects are ambulatory, community-dwelling men over the age of 65 years, separated into two observation groups based on bioavailable testosterone levels. The hypothesis is that older men with low levels of bioavailable testosterone will have increased bone loss. Fifty-five men have been enrolled and bone biopsies have been obtained. No data analysis is available at this time.